#include <stdio.h>
#define PI 3.14159

double volume_tc(double r_lower, double r_upper, double h);

int main(void)
{
    double h, r_lower, r_upper, v;

    scanf("%lf%lf%lf", &r_lower, &r_upper, &h);
    v = volume_tc(r_lower, r_upper, h);
    printf("%.2f\n", v);

    return 0;
}

double volume_tc(double r_lower, double r_upper, double h)
{
    double result = 0;
    result = 1.0/3 * PI * h * (r_lower * r_lower + r_upper * r_upper + r_lower * r_upper);
    return result;
}
